The present invention relates generally to horizontal directional drill machines. It relates particularly to a stakedown assembly for a horizontal directional drill machine.
A horizontal directional drill machine is a common and well-known machine for installing pipes beneath the ground and generally parallel to the surface. These machines are used in many different applications and are available in a wide range of sizes. Typical applications where a horizontal directional drill machine might be used include the installation of fiber optic cables, electrical cables, gas lines, water systems, or sewer systems. Horizontal directional drill machines are commonly rated in terms of pull-back capacity. Some machines for smaller applications have as little as five thousand pounds of pull-back capacity. Other machines are available with a pull-back capacity of as much as one million pounds of pull.
One alternative to a horizontal directional drill machine is the traditional trencher machine. A trencher machine simply digs a trench into the ground, and after (for example) pipe is laid down in the bottom of the trench, the trench is filled and the pipe is buried. The advantage of a horizontal directional drill machine over a trenching machine is that a pipe can be buried in the ground over long distances without digging a trench. Thus, a horizontal directional drill is particularly desirable when a trench would be difficult or too costly to dig. For example, a horizontal directional drill machine finds particularly advantageous application for installing pipes under roadways, where destruction of the road is expensive and inconvenient to travelers, or under a waterway like a river, where trenching would be impossible.
A unique aspect of a horizontal directional drill machine is the special drill head that is attached to the front end of a pipe to be laid. The drill head has an angled shape which allows the operator to change the direction of the pipe after it has entered the ground. Direction changes are achieved by stopping the pipe and drill head rotation and orienting the drill head at a desired angle. Then, by pushing on the drill pipe without rotating it, the drill head and attached pipe will veer in the desired direction. Thus, by effecting directional changes to pipe travel, a pipe might enter the ground at an angle, travel horizontally over a long distance, and re-exit the ground at another angle. This ability to steer the direction of pipe travel also allows the operator to steer the pipe around underground obstacles like boulders.
In addition to pushing forces that must be applied to the pipe as it is inserted, it is often necessary to pull back on the pipe. This may be necessary when a direction change is not completely successful on the first attempt, or when an underground obstacle like a boulder is encountered. The machine then pulls the pipe and drill head back to permit a direction change.
The push and pull forces that are a horizontal drill machine must apply to the drill pipe frequently exceed the weight of the machine itself. Therefore, a system is required to anchor the machine and resist these large forces. The most common system for anchoring the drill machine comprises the use of stakes mounted on the machine body which are screwed into the ground. The stakes have fighting on their tips and are driven into the ground by applying simultaneous rotational and vertical forces to each stake. To drive and remove these stakes, a shakedown assembly is conventionally provided on the end of the drill machine where the drill head enters the ground.
The stakedown assembly includes a drive head that applies the rotational and vertical forces necessary to install the stakes into the ground. A common method of providing vertical force to the drive head is the use of a hydraulic cylinder. Typically, the hydraulic cylinder is pivotally connected at its bottom end to a fixed point on the stakedown assembly. The top end of the hydraulic cylinder is pivotally attached to the drive head which is able to slide longitudinally along a tower. Thus, by operating the hydraulic cylinder, the drive head travels up and down the tower as desired.
Stakes are commonly driven into the ground to a depth of about three feet for optimal holding strength. The drive head, therefore, must be designed to supply this amount of vertical travel. With the type of drive head previously described, a long hydraulic cylinder with a travel length matching the desired stake depth must be provided along with a tall tower and drive head to accommodate the full travel. Because of the overall height of this type of stakedown assembly, which can become quite tall, it is desirable to have a stakedown assembly that could provide the necessary vertical travel distance to the stake but with a smaller overall height.
It is an object of the invention to provide a stakedown assembly which multiplies the travel distance of the hydraulic drive cylinder so that the drive head travels twice the distance of the hydraulic cylinder.
According to the invention, the bottom end of the hydraulic cylinder is pivotally attached to a tower at a fixed connection point along the bottom side of the tower. A gear pinion is pivotally attached to the top end of the hydraulic cylinder with a pivot shaft and a clevis. A first gear rack is fixedly attached to the tower, and a second gear rack is fixedly attached to the drive head. The gear pinion floats between the two gear racks, and when the hydraulic cylinder is actuated, the drive head travels twice the distance of the cylinder. Therefore, a shorter travel hydraulic cylinder is required, and the overall height of the stakedown assembly can be smaller. To maintain proper distance between the gear racks, rollers are pivotally attached to the drive head and contact the tower along its front side to maintain a minimum allowable distance between the gear racks. Shims are attached to the drive head along the back side of the tower to maintain a maximum allowable distance between the gear racks.